The present invention relates to an optical wavelength division multiplex (WDM) system and a method thereof, which are applied to an optical multiplex communication.
A conventional optical WDM system generally has a structure, in which cutoff shifted fibers or dispersion compensation fibers (CSF/DCFs), optical amplifiers and optical wavelength dividers are connected in series, and an optical wavelength division is performed.
FIG. 1 is a block diagram showing a conventional structure of an optical WDM system. As shown in FIG. 1, this conventional optical WDM system consists of a structure, in which eight CSF/DCFs 11 to 18, three optical amplifiers 21 to 23 and eight optical wavelength dividers 31 to 38 are connected in series. In this conventional example, as input signals, eight optical wavelengths xcex1 to xcex8 are used.
An optical wavelength multiplexed signal is inputted to the first CSF/DCF 11 of this conventional WDM system. At the CSF/DCFs 11 to 18, either cutoff shifted or dispersion compensation operation is performed for the inputted optical wavelength multiplexed signal. And the performed signal at the first CSF/DCF 11 is outputted to the optical amplifiers 21 and the amplified signal is outputted to the first optical wavelength divider 31. And this operation is performed in sequence.
At the optical wavelength dividers 31 to 38, only a designated optical wavelength is extracted. The remaining optical wavelength multiplexed signal not transmitted through the optical wavelength dividers is inputted to the next CSF/DCF. This operation is continued until all designated optical wavelengths are extracted at the designated optical wavelength dividers.
Japanese Patent Application Laid-Open No. HEI 9-116493 discloses an optical WDM system, in which one optical coupler performs the division of three optical wavelengths. And Japanese Patent Application Laid-Open No. HEI 9-326759 discloses an optical wavelength dividing apparatus for optical WDM system, in which dispersion compensation and loss compensation are performed efficiently. And Japanese Patent Application Laid-Open No. HEI 10-145298 discloses an optical wavelength dividing apparatus for optical WDM system, in which dispersion compensation and loss compensation are performed efficiently and the number of active devices is reduced.
However, at the conventional examples mentioned above, when a trouble occurs at one optical wavelength divider in the optical WDM system, the trouble also influences the other optical wavelength multiplexed signals transmitted through the optical WDM divider. As a result, abnormal communication occurs at a designated optical wavelength and even at optical wavelengths except the designated wavelength, and the quality of the communication is deteriorated. Moreover, there is a problem that only either one of cutoff shifted or dispersion compensation operation is performed due to the structure.
It is therefore an object of the present invention to provide an optical wavelength division multiplex (WDM) system and a method thereof, in which a trouble of an optical wavelength divider in the system does not influence the other optical wavelengths except a designated optical wavelength that is operated at the optical wavelength divider where the trouble occurred.
According to a first aspect of the present invention, for achieving the object mentioned above, an optical wavelength division multiplex (WDM) system provides an optical coupler in which inputted one optical wavelength multiplexed signal branches into xe2x80x9cnxe2x80x9d optical wavelength multiplexed signals, in this xe2x80x9cnxe2x80x9d is an integer being two or more, and xe2x80x9cnxe2x80x9d optical wavelength dividers, to which said branching xe2x80x9cnxe2x80x9d optical wavelength multiplexed signals are inputted, and in which each of said xe2x80x9cnxe2x80x9d optical wavelength dividers extracts a required optical wavelength signal from said branching optical wavelength multiplexed signals respectively, and which output the extracted optical wavelength signals. And the WDM system connects said optical coupler to said xe2x80x9cnxe2x80x9d optical wavelength dividers, and makes each one of said branching xe2x80x9cnxe2x80x9d optical wavelength multiplexed signals and each one of said xe2x80x9cnxe2x80x9d optical wavelength dividers a pair respectively, and makes optical wavelength multiplexed signal dividing operation between said one optical wavelength signal to be outputted from said one optical wavelength divider and said the other optical wavelength signals to be outputted from said other optical wavelength dividers independent mutually.
According to a second aspect of the present invention, in the first aspect, an optical WDM system further provides an optical amplifier which amplifies said inputted optical wavelength multiplexed signal, and cutoff shifted fibers (CSFs) which perform cutoff shifted operation or dispersion compensation fibers (DCFs) which perform dispersion compensation operation.
According to a third aspect of the present invention, in the first aspect, said one optical coupler connects to a plurality of optical wavelength dividers in parallel.
According to a fourth aspect of the present invention, an optical WDM system provides an optical amplifier which amplifies an inputted optical wavelength multiplexed signal and outputs the amplified optical wavelength multiplexed signal, a first optical coupler which is connected to said optical amplifier and to which said amplified optical multiplexed signal outputted from said optical amplifier is inputted, and in which said amplified inputted optical wavelength multiplexed signal branches into xe2x80x9cnxe2x80x9d optical wavelength multiplexed signals, in this xe2x80x9cnxe2x80x9d is an integer being two or more, a first cutoff shifted fiber or dispersion compensation fiber (CSF/DCF) and a second CSF/DCF which are connected in parallel to said first optical coupler, and to which said branching xe2x80x9cnxe2x80x9d optical wavelength multiplexed signals are inputted by the requirement of the cutoff shifted operation or dispersion compensation operation respectively, and perform the cutoff shifted or dispersion compensation operation for said branching xe2x80x9cnxe2x80x9d optical wavelength multiplexed signals, a second optical coupler which is connected to said first CSF/DCF, in which said branching optical wavelength multiplexed signals inputted from said first CSF/DCF branch into said required number of optical wavelength multiplexed signals, a third optical coupler which is connected to said second CSF/DCF, in which said branching optical wavelength multiplexed signals inputted from said second CSF/DCF branch into said required number of optical wavelength multiplexed signals, the number of optical wavelength multiplexed signals inputted to said second optical coupler-1 CSF/DCFs which are connected in parallel to said second optical coupler, the number of optical wavelength multiplexed signals inputted to said third optical coupler-1 CSF/DCFs which is connected in parallel to said third optical coupler, and xe2x80x9cnxe2x80x9d optical wavelength dividers which are connected in parallel to said number of optical wavelength multiplexed signals inputted to said second optical coupler-1 CSF/DCFs and to said number of optical wavelength multiplexed signals inputted to said third optical coupler-1 CSF/DCFs and to directly said second optical coupler and said third optical coupler respectively.
According to a fifth aspect of the present invention, an optical WDM method provides the steps of branching into xe2x80x9cnxe2x80x9d optical wavelength multiplexed signals for inputted one optical wavelength multiplexed signal, in this, xe2x80x9cnxe2x80x9d is an integer being two or more, dividing said optical wavelength multiplexed signal into xe2x80x9cnxe2x80x9d respective required optical wavelengths, by inputting said branching xe2x80x9cnxe2x80x9d optical wavelength multiplexed signals and extracting each required optical wavelength signal from said optical wavelength multiplexed signals and outputting the xe2x80x9cnxe2x80x9d extracted optical wavelength signals respectively, connecting said branching process to said dividing process, and making each one of said branching xe2x80x9cnxe2x80x9d optical wavelength multiplexed signals and each one of said xe2x80x9cnxe2x80x9d optical wavelength dividing processes a pair respectively, making optical wavelength multiplexed signal dividing process between said one optical wavelength signal to be outputted from said one optical wavelength dividing process and said the other optical wavelength signals to be outputted from said other optical wavelength processes independent mutually.
According to a sixth aspect of the present invention, in the fifth aspect, an optical WDM method further provides the steps of amplifying said inputted optical wavelength multiplexed signal, and cutoff shifted processing or dispersion compensation processing for said branching xe2x80x9cnxe2x80x9d optical wavelength multiplexed signals.
According to a seventh aspect of the present invention, in the fifth aspect, dividing said optical wavelength multiplexed signal into xe2x80x9cnxe2x80x9d respective required optical wavelengths is a process composed of a cascade connecting, and this cascade connecting includes a distributing parallel connecting.
According to a present invention, an optical WDM method provides the steps of amplifying an inputted optical wavelength multiplexed signal and outputting the amplified optical wavelength multiplexed signal, branching into xe2x80x9cnxe2x80x9d optical wavelength multiplexed signals for said amplified optical wavelength multiplexed signal outputted from said optical amplifying process and outputting said branching xe2x80x9cnxe2x80x9d optical wavelength multiplexed signals, in this, xe2x80x9cnxe2x80x9d is an integer being two or more, performing cutoff shifted operation or dispersion compensation operation for said branching xe2x80x9cnxe2x80x9d optical wavelength multiplexed signals by the requirement of the cutoff shifted operation or dispersion compensation operation respectively, and outputting optical wavelength multiplexed signals operated cutoff shifted or dispersion compensation to respective branching processes, branching into required number of optical wavelength multiplexed signals for optical wavelength multiplexed signals inputted from said cutoff shifted or dispersion compensation processes and outputting optical wavelength multiplexed signals, dividing xe2x80x9cnxe2x80x9d optical wavelength multiplexed signals into individual optical wavelength signal and outputting them, in which xe2x80x9cnxe2x88x922xe2x80x9d of them are outputted from performing cutoff shifted operation or dispersion compensation operation and two of them are outputted from said branching processes directly.